The goal of the proposed research is an understanding of the organization and function of the Y chromosome of Drosophila melanogaster, and the role of this chromosome in the regulation of spermatogenesis. Previous studies have focused on genetic, ultrastructural and biochemical aspects of this problem. We now propose to isolate and characterize Y-specific and/or Y-linked DNA. The Y chromosome carries 6 genes (fertility loci) which are inaccessible by methods previously engaged to isolate them. Therefore, this proposal describes novel approaches to the isolation of these genes. These approaches are (1) enrichment of Y chromosome sequences by competitive hybridization between male and female DNA, (2) satellite junction DNA cloning and characterization, (3) cDNA cloning of testes specific RNA, (4) chromosome walking across a translocation from a previously cloned gene into a fertility locus, (5) isolation of Y-loop DNA by differential nuclease digestion. The information gained from the isolation and characterization of these cell specific genes can provide significant contributions to two basic areas of biological investigation: (1) gene and chromosome structure and function and (2) regulation of cellular differentiation.